Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-2...Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.展开更多
In this paper, the synthetic effect ofCr, Mo and Y on corrosion resistance was explored, and the YCr/Mo value was employed to evaluate the corrosion resistance. The composition of amorphous alloy was designed by mixin...In this paper, the synthetic effect ofCr, Mo and Y on corrosion resistance was explored, and the YCr/Mo value was employed to evaluate the corrosion resistance. The composition of amorphous alloy was designed by mixing the Fe41Co7Cr15Mo14C15B6Y2 （BMG1） with good glass forming ability （GFA） and Fe50Cr22B23Ni5.4 with a high corrosion resistance at 9：1 ratio. At the same time, the contents of Y, Mo and Cr were fine-tuned. The electrochemical tests demonstrated that the passivation current density decreased with the increase of the yCr/Mo value. The passivation current density of Fe-based amorphous alloy was reduced by about half an order of magnitude. The fitting result showed that the logarithm ofpassivation current density （I） and the YCr/Mo value （X） were logarithmic relationship, and the fitting equation was I=-5.649＋4.904× 1015 e 17.52x. The X-ray photoelectron spectroscopy （XPS） results showed that the yC,/Mo value played a key role in stability of passive films. When the yCr/Mo value Was low, the Cr6＋ ion, Mo6＋ ion were enriched in the initial stage of passivation process, then leading to the increase passivation current density. However, when the YCr/Mo value was high, the low-valence Fe2-, Cr3＋, and Mo4＋ ion were enriched more easily, which result in small passivation current densities and more stable passive films.展开更多
The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differ...The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differential method.The results showed that the passive film-induced stress and the susceptibility to SCC decreased with increasing pH values when pH≤7,while they increased with increasing pH values when pH7.However,the corrosion type was interpreted as exfoliation corrosion when pH=l and 14,and there was no film formed on the surface of the specimens.The whole variation plots of film-induced stress and the SCC susceptibility with pH values were both presented as a valley shape.The symbol and amount of the film-induced stress were related to the compositions of the passive film,which were analyzed using X-ray photoelectron spectroscopy（XPS）.展开更多
基金supported by the National Natural Science Foundation of China (Nos.51471034,51131001 and 51171025)
文摘Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.
基金Project supported by the National Natural Science Foundation of China(51261021)Science and Technology Landing Plan Project of Jiangxi Province(KJLD13056)
文摘In this paper, the synthetic effect ofCr, Mo and Y on corrosion resistance was explored, and the YCr/Mo value was employed to evaluate the corrosion resistance. The composition of amorphous alloy was designed by mixing the Fe41Co7Cr15Mo14C15B6Y2 （BMG1） with good glass forming ability （GFA） and Fe50Cr22B23Ni5.4 with a high corrosion resistance at 9：1 ratio. At the same time, the contents of Y, Mo and Cr were fine-tuned. The electrochemical tests demonstrated that the passivation current density decreased with the increase of the yCr/Mo value. The passivation current density of Fe-based amorphous alloy was reduced by about half an order of magnitude. The fitting result showed that the logarithm ofpassivation current density （I） and the YCr/Mo value （X） were logarithmic relationship, and the fitting equation was I=-5.649＋4.904× 1015 e 17.52x. The X-ray photoelectron spectroscopy （XPS） results showed that the yC,/Mo value played a key role in stability of passive films. When the yCr/Mo value Was low, the Cr6＋ ion, Mo6＋ ion were enriched in the initial stage of passivation process, then leading to the increase passivation current density. However, when the YCr/Mo value was high, the low-valence Fe2-, Cr3＋, and Mo4＋ ion were enriched more easily, which result in small passivation current densities and more stable passive films.
基金Funded by the National Natural Science Foundation of China(No.51371039)
文摘The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differential method.The results showed that the passive film-induced stress and the susceptibility to SCC decreased with increasing pH values when pH≤7,while they increased with increasing pH values when pH7.However,the corrosion type was interpreted as exfoliation corrosion when pH=l and 14,and there was no film formed on the surface of the specimens.The whole variation plots of film-induced stress and the SCC susceptibility with pH values were both presented as a valley shape.The symbol and amount of the film-induced stress were related to the compositions of the passive film,which were analyzed using X-ray photoelectron spectroscopy（XPS）.
